To put it another way, once the second stage is firing the rocket is more or less in space. There is no SRB to pose an explosion hazard and the fuel is seperate so it can't explode either, there is no air outside so the fuel cannot burn if vented unless oxidizer is vented too. Even if oxidizer and fuel mix, they aren't contained (even by atmospheric pressure) and so cannot explode, only go poof. Max Q is long past, so massive structural failure is extremely unlikely.

Highly visible launch failures always end in explosions because the range safety systems intentionally blow up the rocket (and sometimes SRBs do too) but we never hear about upper stages exploding in space. They generally fail by shutting down or running out of fuel, stranding the payload in the wrong orbit, or fail to separate.

So given that an out of control upper stage could out run any in space designed spacecraft thrust unit the minimum design of an attached spacecraft thrust unit would for final orbit insertion and de-orbit maneuvers correct?

Stated another way after second stage ignition and LAS jettison, if the upper stage fails catastrophically or cannot be shut down the crew would be in trouble.

While our approach would save the crew in that contingency it has a price in terms of weight to orbit regardless of whether we partially fire the LAS motors on ascent or not. If everyone is fine with the above failure scenario no need to penalize our approach.

Not a credible failure. Do you actually think Apollo ignored this? Same with Gemini. Shutting down engines is easy. Ask Elon Musk. All engines use valves that need power to stay open. Remove power (multiple ways of doing this) and the engine shuts down.

Actually on Apollo there was a memo that seriously questioned whether a safe abort was possible in the event of a main engine failure shortly after lift off and that was based on just the minimum time for the system to perform and escape the shock wave. Even after a complete system failure in Apollo 12 they still didn’t pull the handle. There is strong reluctance to chuck billion dollar vehicles at every little indicator light or bump.

In summary crew threatening second stage failures after LAS jettison are deemed to be to remote to worry about. That’s fine by me. I’m sure there will be more pressing issues to deal with between the Moon and back.

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“Do we want to go to the moon or not?”John C. Houbolt - November 15, 1961Question posed in Letter to Dr. Robert C. Seamans Jr, NASA Associate Administrator

What most people ignore here is that none of us are proposing reducing NASA’s budget. NASA’s money in the end pays for jobs. If we spend a lot on SDLV those jobs will be the current jobs tied up in shuttle with very little spent on the exploration end. If we choose a cheaper alternative launch architecture, NASA will be able to afford more in-space and lunar/Mars work. Once again this means jobs, not the shuttle jobs but new jobs. This change scares people.

What needs to be remembered is that NASA’s money will wind up enabling jobs regardless of the architecture. With this in mind, we really should be seeking an architecture that creates results, actual astronauts on the lunar surface. Crewed missions to Mars. All while not sacrificing the unmanned science. A NASA that is showing America’s exploration preeminence is much more likely to get Congresses support than a NASA that can barely support ISS.

I think that, although CEV / CALV architecture might in my humble opinion need to evolve, this architecture will create results. Then we need more: a lunar base, then, many years from now, a Mars base; an ISS evolution (from both the European and the American standpoint).

SMetch - 3/7/2006 9:34 AMExplain to me how an upperstage, which needs to be throttled back so as not over accelerating a combinded vehicle beyond 3g’s, does not over take a vehicle at its nose with a thrust to weight less than ˝ g.

This has always been a problem. Even during Apollo the crew would have been killed after the LAS jettison if the 2nd stage could not be shut down. Given an explosive event in the 2nd stage they would be dead again with the SM engine not capable of getting outside the range of explosion in time. Either way this has always been a dangerous condition which our solution will solve and at the same time not require carrying the complete weight of the LAS to orbit. It’s amazing how this danger zone is somehow ignored when discussing steps that must be taken to “man-rate” a vehicle. In fact this means that for half of the manrated ascent the crew will die, go figure.

How is a second stage going to explode? There is instantly available stored energy in the PV of the thrust chamber, PV of the ullage volume in the fuel tanks, and kinetic energy of the moving engine parts. There's less instantly available chemical energy in the propellant flow, and even less available chemical energy in the stored propellant.

The amount of energy available in the first three sources is not enough to damage the payload (as can be seen by the second Delta III failure), and the latter two sources of energy can't be released fast enough to cause an explosion, at least not during upper stage flight. Shutting down the engines is easy; a combination of spring-loaded normally-closed main propellant valves, shaped charges on the chamber, and pyrotechnically actuated vents on whatever the source for turbine drive gas is will do the trick.

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California 2008 - taking rights from people and giving rights to chickens.

Here's an interesting question: Does the SM of the CEV have enough delta-V to save it if it were stranded on a lofted trajectory by an EELV failure? If the SM fails, the crew will be lost anyway, might as well count on it to save the crew in an emergency - 1500m/s delta-V is quite a bit for use in a pinch.

Here's an interesting question: Does the SM of the CEV have enough delta-V to save it if it were stranded on a lofted trajectory by an EELV failure? If the SM fails, the crew will be lost anyway, might as well count on it to save the crew in an emergency - 1500m/s delta-V is quite a bit for use in a pinch.

The lofting can be solved - requires either reduced payload or additional upper-stage thrust. Lockheed explicitly considered both, I'm not sure what Boeing did. In any event, the current CLV/CEV combo relies on the SM motor during aborts to keep the capsule out of the North Atlantic during winter.

What could, and probably should (IMHO) be done, is to provide triple-redundant IMU/RCS so that they can control the entry and fly a lifting trajectory. This would pay off especially well with the biconic/ellipsled entry vehicles and their higher L/D.

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California 2008 - taking rights from people and giving rights to chickens.

The lofting can be solved - requires either reduced payload or additional upper-stage thrust. Lockheed explicitly considered both, I'm not sure what Boeing did. In any event, the current CLV/CEV combo relies on the SM motor during aborts to keep the capsule out of the North Atlantic during winter.

What could, and probably should (IMHO) be done, is to provide triple-redundant IMU/RCS so that they can control the entry and fly a lifting trajectory. This would pay off especially well with the biconic/ellipsled entry vehicles and their higher L/D.

The lofting can be solved - requires either reduced payload or additional upper-stage thrust. Lockheed explicitly considered both, I'm not sure what Boeing did. In any event, the current CLV/CEV combo relies on the SM motor during aborts to keep the capsule out of the North Atlantic during winter.

What could, and probably should (IMHO) be done, is to provide triple-redundant IMU/RCS so that they can control the entry and fly a lifting trajectory. This would pay off especially well with the biconic/ellipsled entry vehicles and their higher L/D.

there will be a backup RCS/control system on the CEV

But not a full-flegded backup RCS/control system. In the ESAS report, they used the requirement for passive entry to eliminate slender body re-entry vehicles, but then when it turned out that they couldn't guarantee safe re-entry of the capsule, they added the back-up RCS.

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California 2008 - taking rights from people and giving rights to chickens.

The lofting can be solved - requires either reduced payload or additional upper-stage thrust. Lockheed explicitly considered both, I'm not sure what Boeing did. In any event, the current CLV/CEV combo relies on the SM motor during aborts to keep the capsule out of the North Atlantic during winter.

What could, and probably should (IMHO) be done, is to provide triple-redundant IMU/RCS so that they can control the entry and fly a lifting trajectory. This would pay off especially well with the biconic/ellipsled entry vehicles and their higher L/D.

there will be a backup RCS/control system on the CEV

But not a full-flegded backup RCS/control system. In the ESAS report, they used the requirement for passive entry to eliminate slender body re-entry vehicles, but then when it turned out that they couldn't guarantee safe re-entry of the capsule, they added the back-up RCS.

Only if the capsule has shallow side walls, it becomes more stable the closer the CG is to heat shield and the steeper the side walls, just like the Russian capsule.

Either way there must be a DV from the SM that will significantly improve the abort scenarios while minimizing impact on the EELV's optimal lift capabilities. Ideal the DV required for final orbit insertion could be used in an emergency to improve the abort trajectories entry interface location and angle of attack.

Do you have any knowledge along these lines? It would seem the 500 m/s would be enough for just about any scenario.

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“Do we want to go to the moon or not?”John C. Houbolt - November 15, 1961Question posed in Letter to Dr. Robert C. Seamans Jr, NASA Associate Administrator